I agree with everything above and would add ...
Create a steadfast routine with the dogs in your care if boarding in your home. The dogs appreciate and are comforted by this and will recall the routine on return stays.
I have doggy diapers on hand for recent rescues and puppies just in case.
Supervise dogs even when they are outside even in a fenced yard.
Never feed dogs together ... when I have multiple dogs they are separated for feeding and treats. I keep organic, low salt chicken broth on hand for nervous dogs who refuse to eat.
Never take a dog out off leash. I live in a rural area and owners constantly bring their dogs to me off leash and insist their dog will never run off if I do the same. You simply cannot predict a dogs behavior when they are in a new environment.
Good luck!